https://www.youtube.com/watch?v=i536vS3z3e8

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Dimond Bikes Superfan

So, immunity is actually complicated. Here's a good lay explanation by Vox.

One upshot I take from the article is that your immune system relies on 1) antibodies, 2) immune system memory, 3) a few other things like killer T-cells and helper T-cells.

Your BIL tests negative for antibodies now. His immune system may well remember how to fight Covid-19. If he does get infected again, his immune system should mount a more effective response than last time. This isn't guaranteed, but it does seem plausible, maybe even likely based on how the immune system generally works.

The cautions stated in the article header are correct. However, we shouldn't go from the article to giving up hope on vaccines. It does mean that your BIL has to take the same amount of caution as he would have if he hadn't been infected previously. It does not mean that vaccines won't work.

Thanks for the additional links.

I think what I’m coming to understand (and I think is under appreciated the triathlon community) is that vaccines aren’t going to be a light switch moment. We all knew production/distribution of the vaccine would take some time anyhow, but there will also likely be some period of time where we’re all taking additional precautions until we know how long the immunity lasts and how protective the vaccine is.

So even if we have a vaccine by year end, production in Q1, widespread distribution by mid-year, the world still might not look normal. IF there are IMs next summer (and I think that’s the earliest we can reasonably hope for), I wouldn’t be surprised if various social distancing measures are still in place (masked volunteers, crowd controls at expos, additional spacing at start and in transition, etc.). Sigh.....

This does not mean a vaccine an't work.
It's my understanding that vaccines can be tailored to provide a more robust and long lasting immunity than natural infection by influencing the type of immune response that is ellicited. It also seems T-cells show promise even if initial antibody studies haven't.

I’m not suggesting that a vaccine won’t work.

I’m suggesting it’s possible that “immunity passports” from people who have recovered from mild infection may nit be viable, as mild infection might not provide long term immunity.

I'm not an expert, but I believe the same caveats apply. Just because you don't have detectable antibodies does not necessarily mean you have lost immunity. Sure, it doesn't make sense to have a "passport" until we know for sure, though.

I think "antibody passports" are a bad idea anyway as they potentially incentivise people who think they will have a mild infection to try to get infected.

So far, we did ear of stories of second wave hitting the same group of people multiple time... until then, i'm assuming that we have some sort of immunity for at least few months.

Rather than assuming you're covered until you discover otherwise, would it not be wiser to assume you're not unless you have evidence to the contrary?

I don’t know if long-term immunity is a reasonable expectation. There are 4 corona viruses that are associated with the common cold (amongst other viruses). It isn’t like after a few colds you don’t get sick anymore. The virus strain circulate and can reinfect you every few years once your immune response wears off.

I think a totally effective response to Covid-19 will be a vaccine that is ~60-70% effective and an antiviral treatment that lessens the severity if you do get infected. At that point the virus is manageable.

If antibody protection is short lived, then the first place we might see a significant 2nd wave is Sweden. Sweden did not lock down, had a big first wave, but then significant declines in deaths and new cases. Life is close to normal in Sweden, no masks, etc...

Wha we don't know about the virus still exceeds what we do know. Personally, I am not counting on a vaccine. Doing what I can to make sure I'm as healthy as possible, so I am lower risk of a bad outcome should I get COVID (if I haven't already).

We are possibly in the 3rd inning of a 9 inning game, or perhaps a better analogy for this forum, we've finished the swim and have just gotten on the bike. When this is over, it will be interesting to see what we learn from the different approaches taken (Sweden, New Zealand, etc...)

Well... i personally didn't get sick yet... and i ware a mask every time i'm in a public area of any building.

But, socially we have to assume that anti body works for few months, hopefully few years... Otherwise that means that every few months we will all catch that thing (if it didn't kill you the first time, what about the 4 or 5 th time)... and no more racing for any of us.

A very significant decline.

There is another couple of factors for Sweden that probably don't apply to the same level in the USA or UK.
- The drop off strongly coincides with Summer. (a) there is a good link between Temp increase and reduction in both infections, and severity if infected. Not at the level of killing off the virus totally. But still reduces infection and mortality rates. (See if you can get any of the BBC Radio 4 'more or less' podcasts - great stuff for those who like data and cutting through the BS of politicians statistics.)

- Swedes tend to have a much better level of personal responsibility that the UK or USA- so you don't have to legislate to get people to 'switch their brains on' and do sensible things. You didn't see Swedes protesting did you 2" off each other's faces for good reasons. (That behaviour may come with a higher average level of education there than the USA or the UK).

- it's Summer- all the Swedish are out doors grabbing the Vitamin D whilst the sun is available ! And out into the wilds. So less infections. Get away from Stockholm and its a lot less heavily populated = less transmission.


But I do believe in 5 year time we'll see the Swedes got it right.

The declines in Sweden won't be due to any immunity though. If they get a second wave in the short term it will be because behaviour changes rather than immunity wearing off. I don't think anyone was saying they, or anyone else, is anywhere close to herd immunity numbers are they? So at the moment the nature of that immunity isn't the major factor.

Obviously how immunity works is huge in the long term.

This is why the vaccines that are showing cellular and humoral immunity are promising, although I don’t know if the cellular response in the vaccine studes was CD4+ or CD8+ Tcells. The other advantage of vaccination is that a booster shot or two will increase memory cells.

There are some hypothesizing that Sweden may have achieved herd immunity. There is a hypothesis that a significant percentage of the population may have "T Cell" immunity to COVID 19, i.e. because of a prior exposure to another coronavirus the T cells of the immune system have the ability to quickly eradicate the virus. It could be as high as 40% of the population. If another 20% of the population gets the virus and develops antibodies, you're then close to 60% and they may have achieved herd immunity. Of course, if the antibodies only last a few months, and those people don't then develop "T Cell" immunity, then you could see another wave among that groups and the rest of the population.

I am not claiming this is the case, it's a hypothesis. Time will tell. Agree also that seasonality could also play a role (sunlight, vitamin D, etc...), and there are other factors including comorbidities.

Or... did they started to close the economy and ware mask like every body else??

Pretty sure they are still very far from the heard immunity. (60-70% of population)

 





In deaths. Not as much in cases.



Maybe you want New Zealand as an example. Steep drop in both cases and deaths. Although with a grand total of 22 deaths, not much to go on there.

I believe Sweden’s drop in death rate is probably because most of their early infections/deaths were elderly in nursing homes, etc.

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Let food be thy medicine...

I don't understand what you mean. How does assuming something is true, regardless of whether it is or not, benefit society in the long run? It's like you're saying we should pretend everything is fine and either worry about the consequences later, or just deny them.

There are some transmission models which suggest the herd immunity threshold is around 17%. I found this quite interesting, and given the availability of detected case data globally, went and made some state-phase curves to see how close we are to that threshold (vertical black line in the figure below).



So we're quite some way from reaching a measured 17%, but could chalk much of this up to a much wider rate of mild-infections that are not counted because folks are never tested. Many interesting dynamics at play here, for example the roll-over in South Africa only due to reduced testing and not actual lower rates of infection.

Cheers, and keep safe!

Sorry to just skip over the effort you've put into the graph here but 17% makes no intuitive sense to me. Have you got a link to that suggestion?

The only thing I can think is that this is assuming a very low R zero. But R zero would only be very low because of social distancing measures so that would be a very circumstantial herd immunity estimate rather than what most people understand by herd immunity. Or something else I haven't thought of which is why I'm interested in that link. Thanks.

Absolutely; its a great question, source paper here: https://www.folkhalsomyndigheten.se/...ruari-april-2020.pdf

Resultat för ackumulerat antal och andel smittade individer (E+I+R) för de tre scenarierna presenteras i tabell 1. Den 11 april hade totalt 17% av populationen i Stockholms län smittats. Enligt scenario 3 kommer 26% att ha varit smittade den 1 maj. Samtidigt 12 smittsamma (alla som finns i I ), samt peakdagen för de tre olika scenarierna presenteras i tabell 2.


Another: https://www.medrxiv.org/...020.04.27.20081893v3 (hint if thats behind a paywall use scihub).

There is a good summation of this line of thought available here:https://judithcurry.com/...-than-thought/#_edn6

tl;dr: heterogenous (termed inhomogeneity ??) populations is the best explanation we've got for the lower herd immunity threshold.